Melt together chocolate and butter in a medium saucepan until melted and smooth, stirring constantly.

In a separate bowl, whisk together egg yolks, eggs, vanilla, sugar, and salt. Whisk in melted chocolate mixture. Sprinkle sifted flour over the mixture and fold in. Pour batter into each of the prepared dishes.

Bake 20 to 30 minutes (longer for refrigerated batter), checking halfway through the cooking time. The cake batter should rise above the sides of the dishes and the top edges should be dark brown in color. Remove from the oven while the centers are still soft and gooey.

Using a paring knife, run around the sides of the dish to loosen the cakes. Allow cakes to cool at room temperature for 5 minutes.

To plate: Place your dessert plate atop one of the cake dishes. Using oven mitts or a dish towel, hold the plate and the dish together and invert.